The present invention is directed to devices for attaching a suspension system component such as an axle alignment device and/or a load reacting mechanism to the axle housing. In particular, the present invention is directed to axle towers which attach a multifunctional axle aligning and/or load reacting device such as a torque box to the axle housing.
The suspension system of a vehicle provides a comfortable ride for the passenger(s) of the vehicle and protects cargo that the vehicle may be carrying from excessive vibration. Equally, if not more importantly, the suspension system also provides stability to the vehicle by controlling various forces acting on the axle which would otherwise cause an unwanted change in the position of the axle relative to the vehicle frame. Specifically, such forces operate to alter the vertical, lateral, and/or longitudinal position of the axle in relation to the vehicle frame and also can cause axle movement such as roll, yaw, and wind-up. Each of the components of the suspension system reacts and controls one or more of the forces. In order to reduce the complexity and weight of the suspension system, components of the suspension system are being designed to control multiple forces.
A torque box assembly is one such multifunctional component. It reacts to vertical air spring loads, resists braking/acceleration loads, acts as the core roll resisting feature, resists cornering or lateral loading and maintains axle location in relation to the frame rails and also helps to prevent undue yaw and axle wind-up.
In general, the torque box assembly typically comprises a welded steel rectangular box structure. The front and rear ends are welded to round steel tubes. Upon assembly, bonded rubber bushes are inserted into these tubes and round metal rods are placed in the bushings. On one end of the torque box, the rod is connected to a cross member which spans between the frame rails of the vehicle frame. On the opposite end of the torque box, each end of the inner round metal rod is in turn attached to an axle tower linking the torque box to the axle through the axle housing. Further details of a torque box assembly are disclosed in U.S. Pat. No. 6,527,286. The disclosure of U.S. Pat. No. 6,527,286 is incorporated herein by reference.
Clearly, the load path between the axle housing and the torque box is of major import. Attachment devices or axle towers as referred to herein are intended to provide a means of transferring these loads onto the axle housing. These axle towers transfer longitudinal, roll input, lateral and vertical loads. Preferably, the axle towers are capable of this load transfer without overloading and/or fracturing the axle housing.
Asymmetrical axles are the standard in North America. Asymmetrical refers to the fact that the differential housing is offset from the centerline of the axle. Asymmetrical axles present challenges in designing attachment devices that attach axle alignment devices and/or load reacting devices such as torque boxes to the axle housing. The torque box or other device is typically centered between the frame rails of a vehicle and accordingly centered between the opposite ends of the axle. In order to center the torque box or other device, the attachment devices such as axle towers are spaced apart an equal distance from the centerline of the axle. Consequently, since the differential housing is not centered on the axle, the axle towers are typically mounted to the differential housing at different distances from the either side of the centerline of the differential housing. In other words the axle towers are mounted at asymmetric points about the centerline of the differential housing such that a chord connecting the attachment points is not horizontal.
As such, axle towers are typically designed differently from each other to accommodate their asymmetric positioning about the differential housing. Besides having different base configurations due to accommodate the mounting position on the differential housing, the axle towers are also of differing heights in order to maintain the transverse extent of the torque box parallel to the axle at rest. In other words, since one axle tower may be placed at a more elevated position on the differential housing than the other axle tower, that elevated axle tower will shorter than the other axle tower otherwise the torque box will be skewed relative to the axle at rest.
The axle towers have to being able to withstand the stress forces exerted by the torque box or other such devices, the axle towers have to be able to absorb and/or disperse the forces along the axle housing in order to prevent possible failure of the axle and/or differential housings.
Other attachment devices known in the art are perhaps longitudinal and transverse torque rod towers encountered on most on highway suspensions or the tower which connects a “vee rod” to the top of the axle housing. However, these devices are not intended to be multifunctional in nature as is the case with the axle towers of the present invention. The axle towers of the present invention are unique in that they are multifaceted, multifunctional structural components, i.e. structures that react to loads on multiple axes, whereas existing devices are one dimensional in their function, i.e. structures that react to loads on a single axis. In order to provide the functions listed above, several features which are improvements over prior art structures can be included in the axle towers of the present invention.
As will be explained in more detail below, the torque box is in tension and reacts by pulling on the axle towers when a vertical load is applied to the air springs. Due to this cantilevered load into the axle towers, there is a compression side (closest to the torque box) and a tension side (furthest from the torque box) on the axle towers. These two sides of the axle towers therefore can be designed differently to provide an efficient design capable of carrying the loads.
In one embodiment of the axle towers of the present invention, the axle towers can include several features. While these features will be discussed in greater detail below, they are summarized as follows. One feature that may be included is that the compression side of the axle tower differs in shape from tension side of tower. The differing shapes affect the stiffness of each side of the tower and improve the stress distribution and reduce the stress load on the axle housing One difference in the shape in the tower sides is that the side of axle tower that experiences higher compression forces is scalloped or contoured to a greater extent than the other side or tension side of the axle tower.
Another feature that may be included is that slot of the internal connecting plate is asymmetrically shaped. The asymmetry addresses the concentration of stress on one side of the slot through the concentration of material to offset the higher stress level. In other words, there is more material on the side that experiences greater stress forces.
A further feature that can be included is an asymmetrical foot print attaching the axle towers to axle housing. The compression side of the axle tower or the side with the greater degree of cutout or curvature has at least one radiused or rounded corner. The rounded or radiused foot print radius on the compression side of the axle tower attenuates the effects of a sharp corner on the axle housing by distributing the stress load. In addition, the foot print has a sizable extent along the axle housing. This helps to disperse the stress along a larger area of the axle and differential housing.
Yet another feature that may be included is that the scalloping or contouring of the axle tower on the compression side allows it to flex and comply as the axle deforms under load without overloading attaching welds. A structure having no scalloping or contouring would be stiffer and would not flex as the axle distorts which could overload the welds
Yet another feature may be weldment of the axle towers. Weldment is lighter, more cost efficient and may be preferable over common steel casting. In addition, weldment does not require subsequent machining as a casting would. However, the axle tower could be manufactured in casting form versus the fabrication described herein without departing from the scope of the invention. The axle towers of the present invention could also be altered to serve as torque rod attachments.